Cleaning the seas of unexploded bombs, mines and other ordnance is essential but dangerous work. The farther that bomb disposal officers can stay away from explosive devices, the lower the risk they face. This is why the US Navy and other military forces prefer to put underwater remotely operated vehicles (ROVs) in harm’s way. And the chosen vehicle for many is supplied by US-based VideoRay, manufacturer of the Ally, Defender and Pro 5 ROVs.
VideoRay’s products have gained support from the demanding military community because of their combination of small size and portability, high power and lifting ability, flexible payload options, and reliability. And playing an important part in the stability system of the VideoRay ROVs, making remote operation of the vehicle, its video camera and other accessories easier, is the high performance of the Xsens MTi Attitude and Heading Reference System (AHRS) sensor on board.
The Ally, Defender and Pro 5 ROVs operate like a diver, but without putting a human life at risk. Built to a modular design and tethered to a control panel on the surface, the ROV has a 4K camera, optional auxiliary cameras and powerful lights to enable the remote operator to view the scene in detail, and forward-looking sonar to assist with piloting the vehicle in murky water and other low visibility environments.
VideoRay offers a wide range of accessory options for equipping the vehicle with gripping, lifting and other tools. And with seven 1hp thrusters on board, the ROV can move fast through the water and lift heavy objects with ease from the sea floor.
Since the ROV is tethered, it can be remotely piloted. The VideoRay products are widely used by the US Navy on explosive ordnance disposal missions. Here, the ROV navigates semi-autonomously to a zone of interest, heading for destination co-ordinates programmed in by the operator. Once the ROV reaches the zone of interest, a remote pilot takes over to locate the explosive device, and perform the mission’s operation on it. Inertial navigation technology keeps the ROV on track – a combination of a DVL (Doppler velocity log), GPS satellite positioning, Greensea internal navigation software, a pressure sensor for depth measurement, and the Xsens MTi AHRS sensor for tracking the vehicle’s heading. The attitude readings from the sensor also support the operation of the propulsion system, enabling the vehicle to maintain a stable posture underwater.
Andy Goldstein, Chief Technology Officer of VideoRay, explains that the heading measurements are normally the biggest source of error in marine inertial navigation systems. This means that the accuracy of the AHRS has a substantial impact on the ability of the ROV to reliably reach the destination programmed into it. He says, ‘VideoRay’s evaluation of the Xsens MTi AHRS sensor convinced us that its performance would meet the high standards that we set for the inertial system on the ROV. Movella supplies the sensors with a robust software development kit to streamline the system development process. The SDK is also supported by magnetic calibration software supplied by Movella. This means that users can calibrate the sensor’s heading measurements to adjust for variations in the earth’s magnetic field. This fine tuning of the heading system’s outputs is absolutely crucial to the vehicle’s ability to stay on track over missions stretching for hundreds of meters from the starting position.’
The other key factors in VideoRay’s decision to use Xsens MTi AHRS sensors are its size and availability in production volumes. Its small size made it easier for the VideoRay engineering team to fit the sensor inside the compact ROVs, which can be carried by a single person.
The powerful propulsion and reliable autonomous navigation capabilities of the VideoRay ROVs have been tested extensively in thousands of explosive ordnance disposal missions operated by the US Navy and others. The ROVs are also in use in many applications which require their power, portability and flexibility: offshore energy mapping and production, ship maintenance, inspection of underwater assets such as dams, search and rescue and others.
And in all of them, the inertial navigation and handling of the vehicle are assisted in large part by the high-performance Xsens MTi AHRS sensor on board.